1. Field of the Invention
The present invention relates to a magnetoresistive effect element, a magnetic head, and a magnetic disk apparatus which pass a sense current in a direction perpendicular to the film face of a magnetoresistive effect film to detect magnetism.
2. Description of the Related Art
By means of giant magneto-resistive effect (GMR), performance of magnetic devices, magnetic heads in particular, has been rapidly improved. Especially, application of a spin-valve (SV) film to a magnetic head, an MRAM (Magnetic Random Access Memory) or the like has brought a large technological progress to the field of magnetic devices.
A “spin-valve film” is a layered film having a structure of sandwiching a non-magnetic spacer layer between two ferromagnetic layers, and is also referred to as a spin-dependent scattering unit. The magnetization of one (referred to as “pinned layer” or “magnetization fixed layer”) of these two ferromagnetic layers is fixed by an antiferromagnetic layer or the like, and the magnetization of the other one (referred to as “free layer” or “magnetization free layer”) can be turned according to an external magnetic field. In the spin-valve film, by changing relative angles of the magnetization directions of a pinned layer and a free layer, a giant magneto-resistive change is obtained.
As magnetoresistive effect elements using the spin-valve film, there are CIP (Current In Plane)-GMR element, CPP (Current Perpendicular to Plane)-GMR element, and TMR (Tunneling Magneto Resistance) element. In the CIP-GMR element, the sense current is conducted in parallel to the face of the spin-valve film, and in the CPP-GMR and TMR elements, the sense current is conducted in a direction substantially perpendicular to the face of the spin-valve film. The method of conducting the sense current perpendicularly is gaining more attention as a technology corresponding to future high recording density heads.
Here, in the metal CPP-GMR element in which the spin-valve film is formed of a metal layer, an amount of change in resistance due to magnetization is small, and thus it is difficult to detect a minute magnetic field (for example, a magnetic field in a magnetic disk having high recording density).
As the spacer layer, a CPP element using an oxide layer [NOL (nano-oxide layer)] including current paths in a thickness direction is proposed (refer to JP-A 2002-208744 (KOKAI)). In this element, both element resistance and an MR ratio can be increased by a current-confined-path (CCP) effect. Hereinafter, this element is referred to as CCP-CPP element.